Conventional multi-functional tool milling machines often include overarm (a cutter) to support an arbor (a horizontal mill cutter rod), a vertical milling attachment (spindle arm unit) with independent power, that is located in the front end of the overarm (cutter arm spindle), and a (cutter rod support arm) that is attached to the machine body. This, for practical applications, it may only allow to select either vertical or horizontal processing but not both types of processing for continuous processing. Besides, to select the horizontal process, a user is required to dismount the vertical milling attachment (spindle head unit) and therefore it is not convenient for operation. The improvement according to present invention relates to forming a guideway (guide rail) on one side or both sides of a horizontal overarm (cutter rod arm) to couple with a vertical milling attachment unit (vertical cutter spindle head unit) including a keyslotter and a milling attachment (including, for example, milling, boring, drilling, tapping, inserting, grinding spindle head unit) with independent power and enable the vertical milling attachment unit (vertical cutter spindle head unit) including a keyslotter and a milling attachment to shift to and fro for processing and rear locating storage. Thus, when the milling machine is engaged in processing the workpiece horizontally or vertically, the machine body can be easily adjusted to be suitable for processing and further be suitable to continue proceeding in vertical/horizontal process works.